The invention concerns a process for assembling a strip conductor network with an integrated circuit for application to a circuit board of an electro-mechanical clock movement, and also concerns the thus-assembled strip conductor network.
Apparatus and process of this generic type are known from German Pat. No. 26 19 833 as depicted in FIG. 2 of that patent. A strip conductor network for a circuit board is also described in German Pat. No. 3,427,908 corresponding to British Published Application No. 2,163,906 of the present inventor.
It is provided according to German Pat. No. 26 19 833 to bond the circuit (chip) on a strip conductor network cut from a support strip, and bond wiring is connected between the circuit and the respective strip conductors. The network preassembled in this manner is fastened to the insulating support of a circuit board of the clock mechanism. Finally, gaps are cut in the strip conductors in accordance with the required electrical operation of the circuit. (Such gaps were not earlier cut in order to maintain the stability of the network during transfer to the circuit board.) Thereafter, the chip is cast in epoxy. This, however, involves significant restrictions relative to manipulation and also to the configuration of the strip conductors. The environment of the bond wiring between the circuit and the adjacent strip conductors, which is particularly sensitive to mechanical stress, is exposed to appreciable stresses both during the insertion of the network into the circuit board and in the course of the punching out of the remaining bridges, which stresses are capable of leading to functional interference with the bond connections and thus later with the entire electromechanical clock movement.
In view of these shortcomings, it is an object of the invention to improve the processes and apparatuses of this generic type in a manner such that manufacturing complications and operating risks related to the assembly of a circuit board with preassembled strip conductors are reduced, thereby further reducing the manufacturing effort involved in the construction of large clock movements.
This object is attained according to the invention which relates to a process for making a strip conductor network assembly for application to a circuit board of an electro-mechanical clock movement. The process involves providing a strip conductor network including gaps between the ends of selected strip conductors thereof. A circuit chip is adhered to the strip conductor network. Bond wiring is secured between the adhered circuit chip and the strip conductor network. A rigid protective cap is inserted over the portion of the strip conductor network containing the circuit chip and the bond wiring so as to interconnect a plurality of the strip conductors. That portion of the strip conductor network is cut-out, such that the cut-out portion, the circuit board, the bond wiring, and the protective cap together form a unitary member which can be applied to a clock movement circuit board.
Preferably, before the portion of the strip conductor network is cut-out, a molten plastic material is poured into the cap in order to encapsulate therein the strip conductors, the circuit chip, and the bond wiring.
The present invention also concerns the strip conductor network assembly adapted for application to a circuit board of an electro-mechanical clock movement. The network assembly comprises a strip conductor network having gaps disposed between selected strip conductors thereof. A circuit chip is mounted on the network. Bond wiring connects the circuit chip with the network. A protective cap is connected to a plurality of the strip conductors for rigidifying the latter.
Preferably, the interior of the cap is filled with a plastic mass in which the circuit chip and bond wiring are encased.
In accordance with the invention, the cutting of the gaps in the network to form the individual strip conductors required for proper electric operation is carried out prior to the connection of bond wiring and in particular prior to the mounting of the network on its circuit board. This renders it certain that chips are mounted on and bonded to networks which are in their mechanical and geometrical final state and can already have been exposed to appropriate quality control measures (for example, by means of silhouette image processing), so that the possibility of equipping mechanically unusable networks with the expensive circuit chip and bond wiring connections may be avoided from the onset.
The thus-formed network has a chip adhered thereto, and bond wiring is connected between the chip and the strip conductors. Thereafter, the strip conductors are mechanically rigidified and their connecting surfaces and bond wiring are protected by the positive attachment of a cap to the network strip conductors. The cap simultaneously establishes a mechanical connection between the individual strip conductor ends leading to the bond wires and thus counteracts any potential mechanical damage to the bond wire connections due to mechanical bending stress in the course of the further processing of the network.
An additional mechanical protection of the network in the vicinity of the adhesively applied chip and bond wiring is obtained by the injection of a plastic mass (e.g., epoxy) into the cap. The mass, after cooling, intimately surrounds the chip and the bonding wires on the facing surface of the strip conductors, thereby contributing to the mechanical rigidity of the entire structure and to protect same against environmental effects. Preferably, enough plastic material is injected into the opening of the cap so that the strip conductors are surrounded by the solidifying mass even on the side facing away from the circuit and the wiring connections, i.e., the strip conductors are embedded along their surfaces and edges in their solidifying molding material and thereby fixed in their relative orientation.